Occipital plate for cervical fixation

ABSTRACT

An adjustable occipital plate includes a central body portion having a plurality of arms extending therefrom in a generally Y-shaped configuration. Two of the arms include elongate slots for slidably receiving retaining members therein. Each retaining member includes a U-shaped channel for receiving a spine rod and a set screw. The central body portion and one arm include openings for receiving bone screws therein. Each of the arms may be angled with respect to the central body portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to, and the benefit of, U.S.Provisional Patent Application Ser. No. 61/195,825, filed Oct. 10, 2008,the entire contents of which are hereby incorporated by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to devices for bone fixation. Moreparticularly, the present disclosure relates to an occipital plate forcervical fixation.

2. Background of Related Art

The occipitocervical junction, which comprises the occiput, atlas, andaxis, represents a unique and complex interface between the cranium andthe rostral cervical spine. More than 50% of the rotation andflexion-extension of the head and neck occurs in that region. Inaddition, the osseous articulations and their ligamentous supportstructures must resist force in eight axes of rotation. These includeflexion, extension, bilateral lateral bending; and bilateral rotation,distraction, and axial loading. Instrumentation constructs not only mustresist forces in all of these vectors, but also must resist thesignificant lever arm created by the suboccipital bone and the cervicalspine, which meet at a 50° angle. Any instrumentation construct designedfor use in this region must, therefore, have adequate dimensions tointerface with the osseous structures of the spinal structures as wellas have sufficient rigidity and purchase to resist these forces untilbone fusion can occur. Great flexibility must be afforded to allow forthe multiple anatomical variations seen in this region.

In the early 1900's occipitocervical instability and lesions located atthe occipitocervical junction were considered inoperable and terminal.Since the first description of an occipitocervical fusion by Forresterin 1927, multiple methods of fusion in this region have been described.Descriptions of simple onlay bone grafts with halo immobilization; wire,pin, or hook constructs; rigid metallic loops and rectangles fixed tothe bone with either screws or wires; and most recently, plate or rodconstructs with screws have all been described. In general, theevolution of this technology has focused on providing increasingly morerigid constructs to facilitate bone fusion and to minimize the need forand duration of external immobilization.

A common technique for fixing occipitocervical instability is the use ofan inverted Y-shaped screw plate. Using this technique, the plate issecured to C1-2 with transarticular screws and to the suboccipital bonewith paramedian screws. The suboccipital bone varies in thickness, witha mean thickness of about 14 mm. Screws must be carefully selected toprovide adequate purchase, yet avoid cerebellar injury. Utilizing themaximum screw length possible is critical, because shorter screws dohave reduced resistance to pullout. If stabilization is required belowthe C1-2 level, then lateral mass screws can be placed throughadditional holes in a longer plate to include these levels as well. Abone graft is again added to promote fusion. The Y-shaped plate, incombination with transarticular screws, is an economically favorablealternative. Immediate postoperative stabilization is achieved and verylow rates of pseudoarthrosis have been reported.

SUMMARY

The present disclosure relates to an adjustable occipital plate having acentral body portion and a plurality of arms extending therefrom in agenerally Y-shaped configuration. The central body portion and at leastone of the arms include an opening for threadably receiving a bonescrew. Each arm may be joined to the central body portion by a bendablejoint that allows each arm to be individually angled with respect to thecentral body portion.

Further, at least one of the arms includes an elongate slot for slidablyreceiving a retaining member or screw housing. The screw housingincludes a shank having threads formed thereon and a head. The headincludes a pair of opposed upstanding walls defining a U-shaped channeltherebetween that is configured and adapted for receiving a portion of aspine rod. The upstanding walls include threads for threadably engagingthreads of a set screw. Once the spine rod is positioned relative to theoccipital plate and a portion of the spine rod is disposed in theU-shaped channel, the set screw is threaded into the screw housing,thereby securing the spine rod to the occipital plate. The at least onearm including the elongate slot further includes a channel disposed onone side. The channel is configured and dimensioned for slidablyreceiving a nut therein. The nut is threadably engaged with the threadson the shank of the screw housing, thereby retaining the screw housingto the respective arm of the occipital plate. The screw housing may bewelded to the nut and may also be rotatable in the elongate slot sincethe nut may be rotatable within the channel.

A plurality of bone screws is insertable through the openings of theoccipital plate. In one embodiment, the screws are formed from a hardermaterial than the occipital plate. As such, when the bone screws arethreaded into the openings, a lip of each opening deforms such that thebone screw is affixed to the occipital plate and resists backing outfrom the occipital plate.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the presently disclosed occipital plate are describedherein with reference to the accompanying drawings, wherein:

FIG. 1A is a top elevational view of the presently disclosed occipitalplate with rods coupled to retaining members;

FIG. 2A is a top elevational view of the occipital plate of FIG. 1 withbone fasteners disposed in openings of the occipital plate;

FIG. 2B is a side view of the occipital plate of FIG. 2A;

FIG. 3 is an end view of the occipital plate of FIG. 1 with the rodsremoved;

FIG. 4A is a top view of a rod coupled a retaining member;

FIG. 4B is a side cross-sectional view of the rod and retaining memberof FIG. 4A taken along section line 4B-4B; and

FIG. 5 is a side, part cross-sectional view of an arm and the retainingmember of the occipital plate of FIG. 2B.

DETAILED DESCRIPTION

Various embodiments of the presently disclosed occipital plate forcervical fixation will now be described in detail with reference to thedrawings, wherein like reference numerals identify similar or identicalelements. In the drawings and in the description that follows, the term“proximal,” will refer to the end of a device or system that is closestto the operator, while the term “distal” will refer to the end of thedevice or system that is farthest from the operator. In addition, theterm “cephalad” is used in this application to indicate a directiontoward a patient's head, whereas the term “caudad” indicates a directiontoward the patient's feet. Further still, for the purposes of thisapplication, the term “medial” indicates a direction toward the middleof the body of the patient, whilst the term “lateral” indicates adirection toward a side of the body of the patient (i.e. away from themiddle of the body of the patient). The term “posterior” indicates adirection toward the patient's back, and the term “anterior” indicates adirection toward the patient's front. Additionally, in the drawings andin the description that follows, terms such as front, rear, upper,lower, top, bottom, and the similar directional terms are used simplyfor convenience of description and are not intended to limit thedisclosure attached hereto.

Referring initially to FIG. 1, an occipital plate or adjustableoccipital plate 100 is illustrated. The adjustable occipital plate 100includes a central portion 110 having an opening 108 therethrough. Theopening 108 is generally circular and includes a generally circular lip107. In addition, the adjustable occipital plate 100 includes a firstarm 102 and a second arm 104 extending from the central body portion 110at an angle thereto. A third arm 106 also extends from the central bodyportion 110 such that the first arm 102, the second arm 104, and thethird arm 106 define a generally Y-shaped configuration of theadjustable occipital plate 100. In one embodiment, the adjustableoccipital plate 100 is formed from commercially pure titanium. Adeformable joint 114 is located between the central portion 110 and eachof the arms 102, 104, and 106. The joint 114 may be formed such thateach of the arms 102, 104, and 106 are bendable with respect to thecentral portion as shown by directional arrows A in FIG. 3. Thus, thearms 102, 104, and 106 may be bent relative to the central portion 110and define acute angles with respect thereto. Each arm 102, 104, and 106may be individually bent without regard to the remaining arms.

With additional reference to FIGS. 2A and 2B, each of the first andsecond arms 102, 104 includes an elongate oval slot 112, while the thirdarm includes openings 108. Each of the openings 108 is configured forreceiving a bone screw 30 therein. Bone screw 30 includes a shank 32extending from a head. The head of the bone screw 30 preferably includesthreads 36 having a first pitch and the shank 32 includes threads 34having a second pitch that may be different from the first pitch ofthreads 36. In one embodiment, the bone screw 30 is formed from atitanium alloy (e.g. Ti-6A1-4V) or another material that is harder thanthe material used to form the occipital plate 100. In thisconfiguration, when the bone screw 30 is installed in the opening 108,the threads 36 of the head of the bone screw engage the lip 107 of theopening. Since the bone screw 30 is formed from harder material thanthat of the lip 107, the lip 107 deforms, thereby securing the bonescrew 30 and plate 100 to each other. In this arrangement, the bonescrew 30 resists backing out of the opening 108. This type of screwlocking arrangement is disclosed and shown in U.S. Pat. No. 6,322,562 toWolter, the entire contents of which are hereby incorporated byreference herein.

The oval slots 112 are configured for receiving a screw housing 50therein. In this configuration, the screw housings 50 are repositionablethroughout a plurality of positions along a length of the oval slots112. A spinal rod 20 is coupled to each of the screw housings 50.

Referring additionally to FIGS. 4A, 4B, and 5, each screw housing 50includes a head 40 having upstanding walls with internal threads 42 thatdefine a U-shaped channel 44 therebetween. The U-shaped channel 44 isconfigured for receiving the spinal rod 20 therein. The internal threads42 of the head 40 are configured for engaging external threads of a setscrew 52. Each screw housing 50 is secured to its respective oval slot112 by a nut 56.

Further still, the screw housing 50 includes a shank 54 having threadsthereon for engaging the threading of the nut 56. Once assembled, theshank 54 is welded to the nut 56. Since the nut 56 is round, it is ableto rotate in a channel 115 that is located on the underside of the ovalslot 112, thereby allowing the screw housing 50 to rotate relative toits respective arm 102, 104. As such, the screw housing 50 is easilyrepositionable and rotatable for accommodating the spinal rod 20. Thechannel 115 allows the nut 56 and the screw housing 50 to slide alongthe length of the oval slot 112 without the nut 56 separating from thechannel 115. Once the screw housing 50 is in its desired position, thephysician installs the spinal rod 20 in the U-shaped channel 44 of thescrew housing 50. After the spinal rod 20 is positioned in the U-shapedchannel 44, the physician threads the set screw 52 into the head 50 andtightens the set screw 52 which causes the nut 56 and rod 20 to betightened against an upper surface of the respective arm 102, 104 tohold the spinal rod 20 in position. Finally, the physician installs oneor more other bone screws 30 into the openings 108 and secures theadjustable occipital plate 100. Thus, the spinal rod 20 and screwhousing 50 construct is secured to the occiput region of the patient'scranium.

Each of the embodiments described above are provided for illustrativepurposes only. It will be understood that various modifications may bemade to the embodiments of the presently disclosed vertebral bodystaple. By way of example only, it is contemplated that the rodreceiving portion of the housing may include a taper lock for lockingthe rod relative to the housing, rather than a set screw design asshown. A suitable taper lock configuration may be adapted from the taperlock design shown in International Patent Application NumberPCT/US/2008/080682 filed on Oct. 22, 2008 and published as internationalapplication WO 2009/055407, the entire contents of which areincorporated herein by reference. Therefore, the above descriptionshould not be construed as limiting, but merely as exemplifications ofembodiments. Those skilled in the art will envision other modificationswithin the scope and spirit of the present disclosure.

1. A bone fastening assembly comprising: a plate having a centralportion with an opening; a first arm extending from the central portion,the first arm including at least one orifice; a second arm and a thirdarm, the second and third arms extending from the central portion, eachof the second and third arms including an elongated slot; and aretaining member disposed in each of the slots, the retaining memberincluding a housing having a shank extending therefrom and a nut, thenut threadably coupled to the shank such that the retaining member isrepositionable along a length of the slot and retained therein.
 2. Thebone fastening assembly of claim 1, wherein the retaining member issecurable in one of a plurality of positions along the length of theslot.
 3. The bone fastening assembly of claim 1, wherein at least one ofthe second and third arms includes a channel for slidably receiving thenut of the retaining member.
 4. The bone fastening assembly of claim 1,wherein the housing includes a channel for receiving a portion of a rod.5. The bone fastening assembly of claim 4, wherein the nut is threadablycoupled to the shank on the side of the arm opposite the rod receivingchannel.
 6. The bone fastening assembly of claim 4, wherein the housingfurther includes threads for receiving a set screw.
 7. The bonefastening assembly of claim 4, wherein the housing includes a taper lockassembly for securing the rod relative to the housing.
 8. The bonefastening assembly of claim 1, further including at least one bonescrew.
 9. The bone fastening assembly of claim 1, wherein the first arm,the second arm, and the third arm define a generally Y-shapedconfiguration.
 10. The bone fastening assembly of claim 1, wherein atleast a portion of a bone screw is formed from a harder material thanthe first arm.
 11. The bone fastening assembly of claim 10, whereinengagement of the bone screw with the first arm deforms a portion of theat least one orifice such that the bone screw is affixed to the firstarm.
 12. The bone fastening assembly of claim 1, wherein a junctionbetween the central portion and at least one of the arms is deformablesuch at least one of the arms is repositionable with respect to thecentral portion.